We demonstrate that the quantitative conversion of 1-butene to a Schultz-Flory distribution of oligomers has been accomplished by use of Group 4 transition-metal catalysts in the presence of methylaluminoxane (MAO). The oligomerization reaction was carried out at ambient temperature in a sealed reaction vessel with complete conversion of 1-butene at catalyst turnover numbers greater than 17,000. The combination of high catalyst activity without concomitant production of high polymer led to a highly efficient production of new hydrocarbon jet fuel candidates. The reaction proceeds with high regioselectivity; however, because achiral catalysts were used, several diastereoisomeric structures were produced and observed in the gas chromatography-mass spectrometry (GC-MS) chromatograms. The single and specific dimer formed in the reaction, 2-ethyl-1-hexene, was easily removed by distillation and then was itself dimerized using acid catalysis to yield a mixture of mono-unsaturated C16 compounds. Changes in the oligomerization catalyst led to production of fuels with excellent cold-flow viscosity without the need for a high-temperature distillation. Thus, removal of the dimer followed by catalytic hydrogenation (PtO2) led to a 100% saturated hydrocarbon fuel with a density of 0.78 g/mL, a viscosity of 12.5 cSt at −20° C. (ASTM 445), and a calculated heat of combustion of 44+MJ/kg. By back-addition of hydrogenated dimer in varying amounts (6.6, 11.5, and 17 wt %), it is possible to tailor the viscosity of the fuel (8.5, 7, and 6.5 cSt, respectively).
There exist several commercial and research programs around the world aimed at creating full-performance jet fuels based on alternative feedstocks. Traditionally, jet propulsion (JP) fuels contain a complicated array of saturated and aromatic hydrocarbons that are highly refined to meet fuel specifications for a particular application. For instance, the Navy's JP-5 has a significantly higher flash point (60° C.) in comparison to the Air Force JP-8 and commercial jet fuel (about 38° C.). (Corporan, E.; DeWitt, M. J.; Belovich, V.; Pawlik, R.; Lynch, A. C.; Gord, J. R.; Meyer, T. R. Energy Fuels 2007, 21, 2615-2626) (Chang, P. H.; Colbert, J. E.; Hardy, D. R.; Leonard, J. T. Prepr. Pap. Am Chem. Soc., Div. Pet. Chem. 2004, 49, 414). Syntroleum and Sasol have independently produced JP-5 and JP-8 equivalents based on gas-to-liquid (GTL) Fischer-Tropsch processes. (Freeks, R. L.; Muzzell, P. A. Prepr. Pap. Am Chem. Soc., Div. Pet. Chem 2004, 49, 407-410) (Muzzell, P. A.; Feerks, R. L.; Baltrus, J. P.; Link, D. D. Prepr. Pap. Am Chem. Soc., Div. Pet. Chem. 2004, 49, 411-413) and (Lamprecht, D. Energy Fuels 2007, 21, 1448-1453). One of the most challenging aspects to making a jet fuel using Fischer-Tropsch chemistry (Fischer, F.; Tropsch, H. Brennst. Chem. 1923, 4, 276) has been to meet the required coldflow properties. To date, this has required significant postprocessing or “reforming” of the fuel to increase the iso/normal paraffin product ratio. Typically, the Chevron isocracking technology produces a predominance of methyl branching at the 2 position of a hydrocarbon chain; however, the chemical product distribution is quite complicated.
Conversion of propene and butylenes to dimers/oligomers was one of the first commercial processes in the petroleum industry. (Schmerling, L.; Ipatieff, V. N. Adv. Catal. 1950, 21, 2). Some more recent approaches have looked at using mesoporous catalysts and newly designed large-pore acidic zeolite catalysts. (Catani, R.; Mandreoli, M.; Rossini, S.; Vaccari, A. Catal. Today 2002, 75, 125-131) (Schmidt, R.; Welch, M. B.; Randolph, B. B. Energy Fuels 2008, 22 (2), 1148-1155). Transition-metal catalysts (homo- and heterogeneous), generally grouped into the category of Ziegler-Natta (ZN), have enjoyed a successful history for converting olefins, in particular, ethylene and propene, into oligomeric and polymeric materials. (Natta, G. J. Polym. Sci. 1955, 16, 143) (Natta, G.; Pino, P.; Corradti, P.; Danusso, F.; Mantica, E.; Mazzanti, G.; Moraglio, G. J. Am. Chem. Soc. 1955, 77, 1708) (Natta, G. Angew. Chem. 1956, 12, 393. Ziegler, K. Angew. Chem. 1952, 64, 323) (Ziegler, K.; Holzkamp, E.; Breil, H.; Martin, H. Angew. Chem. 1955, 67, 541) (Janiak, C. Coord. Chem. ReV. 2006, 250, 66-94) (Belov, G. P. Petrol. Chem. 1994, 34, 105). Studies using 1-butene can involve a co-polymerization reaction with more reactive olefins, such as ethylene or propene. (Janiak, C.; Blank, F. Macromol. Symp. 2006, 236, 14-22). A study by Kaminsky explored the oligomerization of 1-butene using selected chiral Group 4 transition-metal catalysts and methylaluminoxane (MAO). (Kaminsky, W. Macromol. Symp. 1995, 89, 203-219). In general, the catalysts studied required elevated reaction temperatures and typically led to incomplete conversion of the 1-butene. A study by Christoffers and Bergman reported that using an aluminum/zirconium ratio of 1/1 and with a nearly stoichiometric amount of zirconium “catalyst” that 1-butene could be converted selectively to dimer (2-ethyl-1-hexene). (Christoffers, J.; Bergman, R. G. Inorg. Chim. Acta 1998, 270, 20).
In undertaking this research our goal was to create a full-performance JP-5/tactical biojet fuel that can be derived from a fully renewable and sustainable source of reduced carbon. Carbon dioxide is initially reduced via photosynthesis (e.g., cellulose and triglyceride oils). Further reduction can occur in a second fermentation or microbial treatment to afford an alternative biofuel and/or biofeedstock. (Wright, M. E.; Harvey, B. G.; Quintana, R. Prepr. Pap. Am. Chem. Soc., Fuel Div. 2008, 53 (1), 252-253.)
It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not to be viewed as being restrictive of the invention, as claimed. Further advantages of this invention will be apparent after a review of the following detailed description of the disclosed embodiments which are illustrated schematically in the accompanying drawings and in the appended claims.
It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not to be viewed as being restrictive of the invention, as claimed. Further advantages of this invention will be apparent after a review of the following detailed description of the disclosed embodiments, which are illustrated schematically in the accompanying drawings and in the appended claims.